Can mysql_real_escape_string() Really Prevent SQL Injection Attacks?

SQL Injection Circumventing mysql_real_escape_string()

Despite the widespread belief, it is possible to bypass the mysql_real_escape_string() safeguard in SQL injections. This is particularly concerning because this function is commonly relied upon to protect against such attacks.

The Exploit

An attack demonstrating this vulnerability was outlined in the original post. The key is to exploit a specific sequence of characters ("xbfx27") in conjunction with certain character sets (e.g., gbk). When processed by mysql_real_escape_string() under these conditions, the payload results in an unescaped ' character, which can then be exploited for injection purposes.

The Implications

This vulnerability has far-reaching implications, given the prevalence of mysql_real_escape_string() as a defense mechanism against SQL injections. It affects PHP applications using the mysql_ or PDO_MySQL extensions, particularly when vulnerable character sets are used or PDO's emulated prepared statements are relied upon.

Safe Practices

To mitigate this vulnerability, it is essential to adhere to best practices:

• Migrate to MySQL versions that are not affected by the mysql_real_escape_string() bug (5.1.20, 5.0.22, or 5.1.11).
• Use non-vulnerable character sets for connection encoding (e.g., utf8, utf8mb4).
• Disable emulated prepared statements in PDO (PDO::ATTR_EMULATE_PREPARES).
• Utilize PDO's DSN charset parameter to set the connection encoding correctly in PHP 5.3.6 or later.
• Consider using true prepared statements with PDO or MySQLi, which are not affected by this vulnerability.

By following these guidelines, you can enhance the security of your database applications and protect against SQL injection attacks that attempt to bypass the mysql_real_escape_string() function.

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